Lipopolysaccharide enhances synthesis of brain-derived neurotrophic factor in cultured rat microglia

Expression of neurotrophins in pure microglia cultured from embryonic rat brain and the effects of lipopolysaccharide (LPS) on the expression were investigated. In untreated cultures, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-4/5 mRNAs were detected by use of reverse transcriptase-polymerase chain reaction but NT-3 mRNA was not. LPS stimulation caused a marked increase in BDNF mRNA expression in addition to a slight increment of the NT-4/5 mRNA level; however, the NGF mRNA level was not affected. LPS also increased BDNF-like immunoreactivity in cultured microglia, an action consistent with an elevation of BDNF mRNA. These results demonstrate that LPS stimulates synthesis of BDNF and probably NT-4/5, specific ligands for tyrosine kinase receptor TrkB, suggesting that activated microglia, which appear in the damaged brain, participate in neuronal regeneration via production of such neurotrophins.